ARTICLE Natural graphite reinforced fluoroelastomer composites: Morphological, mechanical, thermal, dielectric, and solvent transport studies Grace Moni 1,2 | Anshida Mayeen 3 | Soney C. George 1 1 Centre for Nanoscience and Technology, Amal Jyothi College of Engineering, Kanjirappally, Kerala, India 2 School of Chemical Sciences, M G University, Kottayam, Kerala, India 3 School of Pure and Applied Physics, M G University, Kottayam, Kerala, India Correspondence Soney C. George, Centre for Nanoscience and Technology, Amal Jyothi College of Engineering, Kanjirappally, Kerala, India. Email: soneygeo@gmail.com Funding information University Grand Commission (UGC), Government of India, Delhi Abstract Fluoroelastomer (FKM) composite embedded with natural graphite (NG) was prepared and its thermal, mechanical, dielectric, and solvent transport proper- ties were explored as a function of NG loading. The morphology of the com- posites was done by AFM, SEM, and TEM analysis, and XRD provides the structural analysis. The composite with 20 phr of NG content showed the highest tensile properties and thermal stability and was supported by fracture surface SEM analysis. Enhancement in polymer-filler interaction in the com- posite was further confirmed by the increase in T g value obtained from DSC analysis. The dielectric permittivity value showed tremendous increment by 30 phr of NG addition with decreased dielectric loss. The resistance to solvent uptake with increase in NG loading by the formation of tortuous pathway is also a clear evidence for the exfoliation of the graphite flakes in the FKM matrix. Better inclusion of NG in FKM matrix efficiently enhanced the ther- mal, mechanical, dielectric and the transport properties of the composites. KEYWORDS fluoroelastomer, mechanical and dielectric properties, morphology, natural graphite, solvent transport 1 | INTRODUCTION Elastomeric composites have viable properties and remarkable design possibilities that make them the supreme materials of present technologies. [1,2] Elasto- mers are predominantly compounded with organic or inorganic fillers to improve the properties according to their need in various industrial areas. [3-6] The outstand- ing properties of fluoropolymers, especially that belongs to the fluoroelastomers such as chemical resistivity, high thermal and electrical stability, mechanical durability, low flammability, low dielectric constant, low surface energy, and low coefficient of friction enabled them to be executed in a range of fields where these peculiar proper- ties are essential. [7] Natural graphite is an allotrope of carbon or the pre- cursor of graphene and it has a layered hexagonal planar structure held together by van der Waals forces, which consists of sp 2 hybridized form of carbon atoms. [8] These peculiarities make graphite an anisotropic material with high thermal and electric conductivities, and at the same time it is also chemically inert and hence used for appli- cations such as pencils, refractory material and electrodes in batteries. [9] The layered structure of graphite is held together in a loosely manner and hence it can be used as a lubricant too. [10,11] Incorporation of graphite into the polymer matrices results in the formation of composites with excellent wear resistance enhanced mechanical, thermal and conductive properties without losing the identity of the polymer matrices. [12] Composites with Received: 11 November 2019 Revised: 22 May 2020 Accepted: 24 May 2020 DOI: 10.1002/pen.25450 Polym Eng Sci. 2020;1–12. wileyonlinelibrary.com/journal/pen © 2020 Society of Plastics Engineers 1